Adds capability to store `pkt_list` for each session packet

[piersoh]

This PR adds a capability to store pkt_list for each session packet which controlled via the store parameter to sniff(). When Scapy is run in session mode it parses the provided pcap/packetlist into "session" packets which have len=None. This PR allows for the storage of the original packets that make up the "session" packets in an attached PacketList as a class variable pkt_list. It is something I have found useful when parsing TCP/HTTP flows.

It was done fairly quickly so happy to be advised on how best to update/modify for better compliance. e.g. I wasn't sure if one should add a field to the Packet type for this or somewhere else?

[gpotter2]

Could you explain what's the use case for this, and add a test that uses it? I also don't see how some parts work.

[codecov[bot]]

Codecov Report

Merging #3058 (a8cc88b) into master (2da3800) will not change coverage. The diff coverage is n/a.

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  Coverage   52.38%   52.38%           
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  Files           9        9           
  Lines        1365     1365           
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  Hits          715      715           
  Misses        650      650           

[piersoh]

I've updated the code to be PEP8 compliant. The self.store is just using the existing store variable/property to activate the pkt_list functionality. As I mentioned I can document this feature if the implementation is agreeable - if not maybe you could suggest a better place/way to store the packet list.

[gpotter2]

Sessions have been changed a lot so this PR is obsolete. Closing.